Tannins from the tree’s bark cured the leather for belts that powered machines that drove the Industrial Revolution. The chestnut’s naturally rot-resistant wood supplied most of the railroad ties and telegraph poles that knitted together the rapidly expanding United States.
‘‘At last when the tree can no longer serve us in any other way,’’ forest economist P.L. Buttrick observed, ‘‘it forms the basic wood onto which oak and other woods are veneered to make our coffins.’’
But by the time he wrote those words in 1915, a death knell had already sounded for the American chestnut.
It is unclear exactly when or how the blight arrived here, though most agree it came on chestnut trees imported from China or Japan. The fungus — Cryphonectria parasitica — was first identified in 1904 by employees of the New York Zoological Park and was soon detected in chestnuts as far south as Virginia.
Entering through wounds in the bark, the fungus threads its way through the straw-like vessels that carry water and nutrients from the ground to the tree’s crown. As the tree responds to plug these holes, the blight works its way around the trunk ‘‘until it is completely girdled,’’ William A. Murrill, the botanical garden’s assistant curator, wrote in 1906.
‘‘The tree essentially commits suicide,’’ said geoscientist Frederick Paillet, an emeritus professor at the University of Arkansas who has studied chestnuts for nearly a half century.
Carried by insects and on the wind, the blight cut through the forests like an invisible scythe. By the mid-20th century, it had spread throughout the entire range — killing an estimated 4 billion trees in one of the worst ecological calamities in U.S. history.
But the American chestnut has not disappeared altogether. Millions of seedlings still sprout each year from old stumps or long-buried nuts. Most reach just a few feet in height before the blight — which persists in the soil and on the bark of surrounding trees — ultimately finds and kills them.
Occasionally, someone will stumble across a tree that has managed to live long enough to flower. Such specimens are referred to as LSA’s — ‘‘large surviving Americans.’’
Last year, Traylor Renfro was clearing trails at his mountaintop retreat in Grassy Creek, near the Virginia border, when something pricked his finger. At first, he thought he'd been stung.
‘‘And then when I looked at it, I realized that it was a bur,’’ he said.
He was aware of the blight, and so his prime suspect was one of the bushlike chinquapins scattered about. His search for more burs led him to a nearby tree, its long, feather-like leaves edged with teeth that resemble breaking ocean waves.
It was an American chestnut — about 37 inches around and at least 50 feet tall.
Nearby, Renfro found several young chestnuts that had sprouted from a desiccated, diseased stump. Examining the larger tree with a ladder, he could see no signs of blight — giving him hope that his tree had somehow developed a defense against the fungus.
‘‘I'm not in denial,’’ he said, cradling a brown bur in his palm as he stared upward. ‘‘But show me one that big.’’
All claims of a naturally resistant American are ‘‘baloney,’’ said Paul Sisco, a retired American Chestnut Foundation staff geneticist. This and other LSA's, he said, have just somehow managed to hang on a bit longer.
‘‘These trees often die within a year or two of ‘discovery,'’’ said Sisco, past president of the foundation’s Carolinas chapter.
But these survivors are playing an important role in the restoration effort.
Soon after the blight was discovered, the U.S. Department of Agriculture began trying to develop a hybrid that was resistant and would grow tall enough to produce marketable timber. Because Chinese and Japanese trees, unlike the American ones, had evolved along with the blight, the emphasis was on crossing native trees with the foreign ones.
‘‘It didn’t matter whether it looked like an American chestnut,’’ said Kim Steiner, a professor of forest biology at Pennsylvania State University. The goal was simply ‘‘some sort of a timber tree.’’
After decades and millions of dollars, the government gave up. To be honest, purists weren’t interested in what the government was after, said Steiner.
‘‘We’re not talking about replacing American chestnut,’’ he said. ‘‘We’re talking about restoring American chestnut.’’
Enter Charles Burnham.
A corn geneticist by training, Burnham was retired from the University of Minnesota when he read about the government’s failed efforts. He began thinking about ways in which his own successful work with food crops might be applied to the chestnut conundrum.Continued...